When you reach Nimbasa City, you'll be able to find the Dropped Item, which is somebody's Xtransceiver. The moment you get this item, you will receive a call on it from the item's owner stating that they would like the Xtransceiver back. They will request to call you at numerous points, but the locations they call you are very specific, only 15 areas each on a specific tile. These are the exact tiles shown below. After a couple of calls, you will learn that the owner of the Xtransceiver is Yancy/Curtis, one of the presenters of a variety of TV programmes in Unova. Yancy will appear if you're male and Curtis if you're female.

Nimbasa City

Route 5

Route 16

Driftveil City

Route 6

Mistralton City

Route 7

Lentimas Town

Undella Town

Route 13

Route 14

Lacunosa Town

Route 12

Route 11

Route 9

Calling them

Once you have had 10 phone calls, they will call you and arrange to meet in Nimbasa City. They will meet you outside the Ferris Wheel and talk to you there. After that, they will register themselves in your Xtransceiver, however they will only appear in certain areas randomly, the same areas as above, but not limited to a single tile.

As you call them, you will have many conversations about a variety of subjects. On the 30th call they'll tell you they want to meet at Nimbasa City where they'll ride the Ferris Wheel with you. Call them to total 50 times, in the 40th call they'll be 'SOUND ONLY', in the 50th call they'll be wearing their work clothes, and cut the line in a second or so.

Trades

Once you have called them anywhere between 30 and 50 times, call the next day and you can meet them outside of the Ferris Wheel where they will trade. They have a variety of Pokémon, whose species depends upon the gender of the character. All these Pokémon have their Hidden Abilities and most aren't available in the Unova Region. You can repeat trades one a day, even repeating the species of the Pokémon.